Review the Trend of Frosty Days in Iran

Document Type : Research Paper

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Abstract

In this study, by the help of interpolated data of  minimum temperature of Iran within the time period of 21, March 1961 up to 19 March 2003, the trend of frosty days in Iran was reviewed and studied.  An array with  dimension 15705*7187   was obtained and  day was inserted on rows and cells on the column. For all the months of the year , the number of frosty days on each cell was counted .Nonparametric   Mann–Kendall test was used for identification of the trend and Linear regression test of least square method was used for calculation of the  trend slope.
 In total, the study results showed that, the number  of frosty days in an extensive area of Iran has a  negative and decreasing trend. These regions located on northwest and also on  even  and plain areas at the  central, eastern and southern part of Iran. Only  on  a small part of  higher elevations including Zagros and Alborz mountain chains, the trend is positive  The most extensive negative trend was observed in January while the most extensive positive trend observed in March. The frosty days in Iran summer and May is fixed and without any trend.
 

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